In the marine industry, a generator set is used for the generation of A.C. electricity when a marine vessel is underway, moored, or anchored. The generator set allows all modern conveniences to be operated on the marine vessel such as air-conditioning, refrigerator, stove, A.C. lights, electric water heaters and so forth.
Small generator sets, used on small boats, are typically powered by a gas engine which present unique problems that can make their use dangerous. The use of gasoline is a volatile fuel which leads to handling and exhaust concerns. Large generator sets employ diesel engines, which are superior to gasoline engines for economy, and are typically found on larger boats due to their size and weight. Ironically, the need for fuel efficient engines is needed by the smaller boats which have limited fuel capacities.
Recently, generator set manufacturers have been able to adapt small diesel engines for use in boats, even if the boats employ gasoline engines for propulsion. For instance, the engine manufacturer known as Kubota builds a horizontal, 4-cycle diesel engine having a single cylinder that produces 7 HP. The applicant has adopted the engine to a generator wherein the combination is capable of producing 3500 Watts while drawing about 2/10 gallons of diesel fuel per hour. The combination disclosed in a previous patent application by the Applicant having U.S. Ser. No. 08/808,880, the contents of which is incorporated herein by reference. The minimal fuel requirement allows even small boats to install a generator and fuel tank. The entire engine and generator requires a space less than 15 inches wide, 15 inches tall, and 28 inches long.
A requirement with any engine that operates in a confined area is the need for cooling. Boats are unique in that cooling may be obtained from the same water that the boat is driven upon. If the water is high in salinity, the diesel engine should also be freshwater cooled. Freshwater cooled means that the engine incorporates a closed circulating coolant, e.g. a mixture of water and an ethylene-glycol type cooling fluid. The cooling fluid interfaces with a liquid-liquid heat exchange device, which is supplied with constantly circulating water, normally designated "raw" cooling-water, from the sea, river, etc., thereby maintaining the engine at a safe operating temperature.
Maintenance of an adequate supply of circulating water is performed by a number of methods, such as an internal pump, a motor driven pump, or an external pump operated on either D.C. power derived from the vessel's batteries, or A.C. power derived from the output of the generator.
The natural position of a motor driven pump would be along an extension from the drive shaft that rotates the generator. However, as previously mentioned, small boats have limited space and the placement of a motor driven pump to the drive shaft will cause an increase in the width of the generator set, which may make it unacceptable for many such boats. In addition, the drive shaft used for rotation of the generator is always positioned in the rear of the generator set as it requires no maintenance and its rotation can be dangerous if exposed. For this reason, the drive portion of a generator set, such as the Kubota, is placed against the hull of a boat with all items of maintenance located along the front of the generator set.
Thus, placement of a motor driven pump along the drive shaft not only increases the width of the generator set but also positions a pump, which must be accessible, in a most unaccessible position. It should be noted that the raw water pump on any engine is subject to normal wear and must be repaired or replaced as needed. If the boat is driven in gritty water, this pump may be replaced frequently.
For the above reasons, diesel powered motors used in small boats typically have an external pump mounted remotely from the generator set. However, this type of operation also presents problems. If the boat is equipped with components such as marine navigational equipment, shower, head, stereo, cabin lights, DC refrigerator, bilge pumps, etc., it is often possible to draw the battery(ies) down to dangerously low levels by adding the constant operation of a cooling-water pump to its load. If the boat owner chooses to operate the cooling-water pump via an A.C. motor, the potential of creating a lethal situation arises. High water in the bilge coupled with the presence of A.C. voltages in the 110-120 volt range can create an environment where electrocution becomes a real possibility. In addition, the use of an A.C. pump requires the generation of electricity, which may not occur for 10 or more seconds after the start of the pump.
Thus, what is needed in the field is a means of providing adequate and dependable flow of raw cooling-water without incurring an undesirable drain on the boat's D.C. power resources, causing a perilous condition due to the presence of A.C. power, or adding to the size of the generator set.